Azlactones (also referred to as 5(4H)-oxazolones or 2-oxazolin-5-ones) have been known for over 100 years and have been intensely investigated as valuable synthetic intermediates. An important and characteristic reaction of azlactones is a ring-opening addition reaction of various nucleophiles, HXR, in the equation (1) below (wherein X=O, S, NH, or NR and R means independent selections of alkyl and/or aryl groups), to provide the corresponding alpha-amidoacetyl derivative. ##STR1## These nucleophilic addition reactions of azlactones have been utilized to prepare a wide variety of alpha-amidoacetic acids and derivatives including esters, amides, and thiolesters.
The facility with which azlactones undergo ring opening reactions with various nucleophiles has also been exploited in polymer chemistry. Reactions of bisazlactones with diamines, diols, and aminoalcohols have been used to prepare polyamides and polyesteramides (see, for example: C. S. Cleaver and B. C. Pratt, J. Am. Chem. Soc., 77, 1541 (1955); M. Ueda, K. Kino, K. Yamaki, and Y. Imai, J. Polymer Sci., Polymer Chem. Ed., 16, 155 (1978); P. P. Policastro and P. K. Hernandez, J. Polymer Sci., Polymer Chem. Part A, 25, 2819 (1987)). Certain of these polyamides derived from the reactions of bisazlactones may be transformed into novel polyimidazolinones by dehydration upon heating (U.S. Pat. No. 4,785,070). Other heterocycle-containing polymers, namely polyamidomethylbenzazoles, are prepared by the reaction of bisazlactones with bis(ortho-substituted aromatic amines) (see U.S. Pat. No. 4,816,554).
2-Alkenyl azlactones have also found broad utility in polymer science, and our recent review entitled "Polyazlactones" (contained in the Encyclopedia of Polymer Science and Engineering, Volume 11, 2nd edition, 1988, pp. 558-571) is incorporated herein by reference. Reaction of 2-alkenyl azlactones with appropriate nucleophiles, as depicted in the general equation above, leads to acrylamide-functional monomers which can be converted into polymers by standard free radical polymerization techniques. Several applications for these polymers in the photographic industry have been described, for example as binders for photographic emulsions to replace a portion of the gelatin typically used in photosensitive silver halide emulsions (U.S. Pat. No. 3,396,030; U.S. Pat. No. 3,713,834; and U.S. Pat. No. 3,721,565) or as base cleavable mordants for improved film processing (U.S. Pat. No. 4,539,383).
Alternative to reaction of 2-alkenyl azlactones with nucleophiles followed by polymerization of the resulting acrylamide-functional monomer is a procedure in which the 2-alkenyl azlactones themselves are homopolymerized or copolymerized with other monomers employing standard free radical polymerization conditions. The resulting azlactone-containing polymers derive significant utility from the presence of the pendant, reactive azlactone group as a site for polymer modification. A method of changing the hydrophilic/hydrophobic character of the azlactone-containing polymer by reaction with appropriate nucleophiles has been described (see U.S. Pat. No. 4,451,619). U.S. Pat. Nos. 4,304,705 and 4,378,411 also teach reaction of azlactone-functional polymers with nucleophiles such as 2-hydroxyethyl methacrylate providing polymers with pendant acrylic functionality. These polymers crosslink upon exposure to actinic radiation via the acrylic sites and become insoluble and are thus useful in the graphic arts. Utilization of pendant azlactone rings of alkenyl azlactone copolymers as reactive sites for crosslinking by reaction with diols or diamines for use in coating compositions has been described (see U.S. Pat. Nos. 3,488,327 and 4,699,843). Azlactone-functional polymer beads useful for attachment of complexing agents, catalysts, or biological materials such as enzymes or other proteins have been described (U.S. Pat. Nos. 4,737,560 and 4,871,824). Reaction of pendant azlactone groups of other 2-alkenyl azlactone copolymers with surface silanol groups on glass provides strongly adherent claddings for optical fibers (see U.S. Pat. No. 4,852,969).
In addition to incorporation of useful azlactone functionality into polymers by copolymerization of 2-alkenyl azlactones, certain amine- and mercaptan-functional oligomers and polymers can be rendered azlactone-functional by a different method, namely by Michael-type addition reactions of the amine or mercaptan groups of the oligomers and polymers to the carbon-carbon double bond of 2-alkenyl azlactones. The resultant azlactone-functional materials are useful for the preparation of polyamides (see U.S. Pat. Nos. 4,485,236 and 4,639,286).